Biology

Slowbro is a bipedal, pink Pokémon with a tan, striped belly and a tan muzzle. It has large, vacant eyes, curled ears, and two pointed teeth in its upper jaw. On its hands, it has three clawed fingers, and two clawed toes on its feet. There is a Shellder attached to its tail. This Shellder has a gray, spiraled shell with darker spots. There are several spikes across the surface of Shellder, and it holds onto Slowbro with many sharp teeth. If Shellder is knocked off, Slowbro will return to its unevolved form.

Slowbro has lost the capability to feel pain due to Shellder's poison. However, it apparently becomes inspired when Shellder bites down. While it is capable of unleashing powerful psychic attacks, it is peaceful and prefers not to fight. Because it can no longer fish using its tail, it swims to catch its prey and allows Shellder to feed on its scraps. Slowbro tends to live near ponds, lakes, and seashores.

When Slowbro Mega Evolves into Mega Slowbro, it becomes engulfed by the Shellder to the point where only its head, arms and tail are visible. The spiral Shellder loses its own tail, allowing the tail of Slowbro to stick out, which it balances on due to its legs being engulfed. The spikes on the Shellder are now reduced to four on the bottom section of its body, and the darker spots only visible on the middle section. Mega Slowbro's energy has gathered in the Shellder clamped onto its tail. As a result, the hardness of its shell is boosted, making an armor so hard that nothing and no one can scratch it. When Mega Slowbro battles, it stands up on its tail. It can move by bouncing along, using its tail as a spring.[1]

In the manga

In the Pokémon Adventures manga

Slowbro's first real appearance was under the ownership of Lorelei in Playing Horsea in Pokémon Adventures where multiple were used for her Ice-type army. With the Shellder clamped onto its tail, Lorelei explains that her Slowbro has sharpened senses and is capable of looking in all directions, thanks to the extra pair of eyes, allowing it to discover Green's ploy using Horsea.

Trivia

Despite it being a commonly known and accepted fact that Shellder triggers the evolution, mentioned in most of its Pokédex entries, Slowbro's evolution from Slowpoke has nothing to do with Shellder in the games, unlike how the evolution of Mantyke requires a Remoraid.

Many Pokémon are noted to evolve by two or more Pokémon combining, such as Metang being formed by two Beldum. However, the anime does not show this and simply spawns the second Pokémon out of nowhere: an example is Morrison's Beldum, which simply evolved into Metang without the need of joining to another Beldum. The evolution of Slowpoke into Slowbro or Slowking is the only time that evolution by two Pokémon physically merging is shown.

Origin

Slowbro's shell and lifestyle are somewhat similar to hermit crabs, though it is physically similar to giant otters, giant salamanders, and hippopotamuses. Slowbro's appearance may also be a reference to the mythical sazae-oni, a magical sea demon of Japanese folklore distinguished by its spiny "sazae" or "turban shaped" snail shell.

Its parasitic relationship to Slowpoke may be inspired by leeches. Interesting enough, Slowbro is known as the Hermit Crab Pokémon and many real-world parasites, including leeches, often target crabs.

Name origin

Slowbro is a combination of slow and bro (short for brother). It may just be used in a general sense, or it could refer to the brotherly/symbiotic relationship shared by the combined form of Slowpoke and Shellder.

Yadoran may be taken to mean 宿らん (to not lodge/dwell). It may also reference 宿借り yadokari (hermit crab) or 宿主 yadonushi ([parasitic] host).